1. Field of the Invention
The present invention relates to a stabilized, cosmetically and/or dermatologically acceptable emulsion intended to moisturize human facial and/or body skin, including the scalp and the nails. More precisely, it contains a fatty phase, an aqueous phase, at least one emulsifying agent and at least one moisturizing agent.
The invention also relates to a cosmetic use of this emulsion to combat ageing of the skin, acne, pigmentation of the skin and/or hair loss, and to a process for moisturizing the skin.
2. Discussion of the Background
The importance of keeping the skin well moisturized, both at the surface and in the deeper epidermal and dermal layers, is fully understood. It is also necessary to supply the skin with moisturizing active agents.
As the skin gets older, various signs of ageing appear on the skin, these being reflected especially in a modification of the cutaneous structure and function. This ageing is physiological in nature but is also photo-induced, that is to say that it is due to the repeated exposure of the skin to light and, consequently, to the formation of oxygenated free radicals by the action of this light on the constituents of the skin.
The main clinical signs of cutaneous ageing are particularly the following: appearance of deep wrinkles which increase with age. Disruption of the "grain" of the skin is observed in particular, that is the microrelief is less uniform and has an anisotropic nature.
Moreover, the complexion of the skin is generally modified; it appears paler and yellower, which appears to be due essentially to disturbance of the microcirculation (less haemoglobin in the dermal capillaries). Many colored blemishes appear at the skin surface, due to impaired melanogenesis. Diffuse irritations, and sometimes telangiectasia, occur in certain areas.
Another clinical sign of ageing is the dry and rough appearance of the skin which is essentially due to more considerable desquamation caused by diffracting light rays. These squama also contribute towards the somewhat grey appearance of the complexion.
Moreover, it is increasingly sought to introduce active agents, for instance vitamins such as vitamins A, B, C, D, E or F, into cosmetic and/or dermatological compositions in order to provide specific treatments against ageing of the skin, its drying, against acne and certain skin diseases (psoriasis), or to promote cicatrization of wounds and/or restructuring of the skin.
In particular, the presence of a sufficient amount of ascorbic acid or vitamin C, especially on the skin, enables stimulation of the growth of connective tissue, and especially that of collagen. Ascorbic acid also enables the cutaneous tissue defenses to be strengthened against external aggressions such as those of ultraviolet radiation, pollution, and drug, alcohol or tobacco aggressions.
However, a certain number of moisturizing reagents such as vitamin C are known to be unstable. For example, B. R. Hajratwala, "Stability of ascorbic acid", Sciences Phamaceutiques Revue (Review of Pharmaceutical Sciences) pages 281-286, teaches that ascorbic acid possesses instability properties in aqueous, aerobic or anaerobic media, with a more pronounced instability in aerobic media.
Illustrations are given therein regarding the behavior of ascorbic acid in particular towards variations in pH of the solution containing it, variations in light, in temperature, and towards compounds such as surfactants, solvents and catalysts, particularly metal catalysts. Such behavior of ascorbic acid in aqueous media leads to the requirement for it to be stabilized. This has already been proposed in Patents JP 89/115,558 and JP 83/129,892, which teach, on the one hand, of blocking the reactive site of ascorbic acid, namely the hydroxyl site, by esterification and/or etherification especially with phosphated, sulphated or alkylated derivatives, and, on the other hand, of the use of these derivatives in cosmetic compositions in order to play the same role as that of vitamin C. This blocking of the active site thus enables ascorbic acid to be rendered more stable; it is, however, less effective than vitamin C in the free state (that is to say containing no additional groups).
Other modes of stabilizing ascorbic acid have been proposed, including esterification of an ascorbic acid derivative, and of a tocopherol derivative, with phosphoric acid (see for example, KAKUJI TOJO and AE-RIC LEE, "Bioconversion of a vitamin to vitamins C and E in skin", J. Cosmet. Chem., vol. 38, pages 333-339). However, the use of this type of diester in cosmetic compositions does not permit ascorbic acid to be released rapidly or in sufficient amounts at the skin surface.
Moreover, ascorbic acid and retinol are known to provoke skin irritations when they are used in cosmetic and/or dermatological compositions, in the free state and at high concentration.
Other active agents, such as nucleotides, are difficult to dissolve. Yet others, such as certain vitamins, are not readily bioavailable.
Moreover, a cosmetic bleaching composition containing a silicone oil, glycerine and magnesium ascorbyl phosphate is known from the document JP-A-05139949. This composition does not allow for good moisturization of the skin.